Abstract

Often the similarity between Ss and objects is judged in a nonsymmetric way. Nearly all methods (multidimensional scaling) assume symmetric data. Nonsymmetries are related to the nonreliability of judgements. Tversky (1976a) proposed a set-theoretic contrast model and focus hypothesis which want to describe and explain nonsymmetric similarity judgements.
It is the purpose of this paper to show that the multidimensional scaling methods can take into account nonsymmetries, too. This is done by proposing a
driftmodel and a comparison hypothesis. The driftmodel incorporates some ideas of Lewin's field theory, whereas
the comparison hypothesis leans heavily on feature matching theory. Both approaches are compared using Rothkopf's Morse code data ("percent-same-judgments"). In the last part of the paper we discuss some psychological and heuristic problems when testing axioms of measurement models.